The present invention relates to polymer nanoparticles, methods for their preparation, and their use as, for example, additives for rubber, and particularly, tire compositions. The invention advantageously provides mechanisms for surface modifications, functionalization, and general characteristic tailoring to improve performance in various polymer compositions.
Polymer nanoparticles have attracted increased attention over the past several years in a variety of fields including catalysis, combinatorial chemistry, protein supports, magnets, and photonic crystals. Similarly, vinyl aromatic (e.g. polystyrene) microparticles have been prepared for use as a reference standard in the calibration of various instruments, in medical research and in medical diagnostic tests. Such polystyrene nanoparticles have been prepared by anionic dispersion polymerization and emulsion polymerization. However, controlling the size of nanoparticles during polymerization and/or the surface characteristics of such nanoparticles can be difficult.
Rubbers may be advantageously modified by the addition of various polymer compositions. The physical properties of rubber moldability and tenacity are often improved through such modifications. Of course, however, the simple indiscriminate addition of nanoparticles to rubber is likely to cause degradation of the matrix material, i.e., the rubber. Nonetheless, it is expected that the selection of nanoparticles having suitable size, material composition, and surface chemistry, etc., will improve the matrix characteristics.
In this regard, development of nanoparticles having a outer layer which would be compatible with a wide variety of matrix materials is desirable because discrete particles could likely disperse evenly throughout the host to provide a uniform matrix composition. However, the development of a process capable of reliably producing acceptable nanoparticles has been a challenging endeavor. For example, the solubility of various monomers in traditional alkane solvents has made solution polymerization a difficult process by which to achieve nanoparticles having a desirable outer layer. Moreover, the development of a solution polymerization process producing reliable nanoparticles, particularly nanoparticles advantageously employed in rubber compositions, has been elusive.
Commonly owned U.S. Pat. No. 6,437,050 is directed to polymer nanoparticles and a method of forming nanoparticles with desired surface characteristics and size. Commonly owned U.S. patent application Ser. No. 10/223,393 (filed Aug. 19, 2002) includes a method of controlling the surface characteristics of polymer nanoparticles via surface functionalization. Each of these is directed to the formation of nanoparticles having uniform sizes and each is herein incorporated by reference. In addition to the nanoparticles disclosed therein, it would be desirable to develop a process for forming polymer nanoparticles with a broad and controllable size distribution. It would also be desirable to develop a batch process for forming polymer nanoparticles with bimodal or trimodal size distributions.